Multiple Deaths As Footbridge Collapses At US University

A new pedestrian bridge collapsed on to a highway at a Miami-area college, crushing at least five vehicles under massive slabs.

Several people were seen being loaded into ambulances and authorities launched search and rescue missions.

Miami-Dade Fire Rescue tweeted that "multiple" people were injured when the Florida International University bridge collapsed on Thursday.

Authorities said they were working on confirming the numbers.

The bridge under construction was expected to open to foot traffic next year.

"We are shocked and saddened about the tragic events unfolding at the FIU-Sweetwater pedestrian bridge. At this time we are still involved in rescue efforts and gathering information," the statement said.

The $US14.2 million ($A18.2 million) bridge crossed over a busy seven-lane road highway that divided the university's campus from the city of Sweetwater.

The 860-tonne span was installed on Saturday to great fanfare.

The main part of the 53-metre span was assembled by the side of the road and had to be moved into place.

The "accelerated bridge construction" method was supposed to reduce risks to workers and pedestrians and minimise traffic disruption, the university said.

Governor Rick Scott tweeted that he was on his way to the scene.

"I will be in constant communication with law enforcement throughout the day," the governor said.

Florida International University is the second-largest university in the state, with 55,000 students.

Most of its students live off-campus and the bridge was supposed to be a safe way to cross a busy street and a plaza-like public space with seating where people could gather.

Florida International University is also home to the National Hurricane Center.